Soil science

Introduction to Soil Science

  • Soil is a complex mixture of minerals, organic material, air, and water that supports plant life.

  • Soil acts as a medium for plant growth by providing nutrients, anchorage space, and water.

Soil Components

  • Minerals form the majority of the soil and come from the breakdown of rocks.

  • Organic matter, such as decomposed plant and animal material, is a key source of nutrients for plants.

  • Soil water is a primary carrier of nutrients for plant absorption and is essential for biochemical processes.

  • Soil air provides the necessary gases for respiration in plants and soil organisms.

Soil Profile and Horizons

  • A soil profile refers to the vertical section of soil from the ground surface to the parent rock, divided into layers called horizons.

  • The O horizon contains organic matter in various stages of decomposition and is typically dark in colour.

  • The A horizon or topsoil is the part of the soil where plants grow most of their roots and is high in organic matter and nutrients.

  • The B horizon or subsoil collects minerals leached from the A horizon, is rich in clay, iron, or aluminium compounds.

  • The C horizon contains parent material like rocks, and has little organic material or life.

Soil Properties

  • Soil texture classifies soil based on the proportion of sand, silt, and clay. Soil texture influences water-holding capacity and nutrient availability.

  • Soil structure describes the arrangement of soil particles into aggregates. Good soil structure promotes water movement and root growth.

  • Soil colour can indicate its mineral and organic matter content. For instance, dark soil tends to be rich in organic matter.

Soil Water

  • The field capacity of soil is the maximum amount of water it can hold after excess water has drained away, crucial for plant growth.

  • Wilting point is when the soil has so little water that plants can no longer extract it.

Soil pH and Nutrient Availability

  • The pH level of soil affects the solubility of nutrients. Most nutrients are readily available in slightly acidic to neutral soil (pH 6 to 7).

  • Soils that are too acidic or alkaline can restrict plant growth due to deficiencies or toxicities of certain nutrients.

Soil Conservation

  • Soil erosion is a major environmental concern as it degrades the land’s productivity by removing the nutrient-rich topsoil.

  • Practices such as intercropping, mulching, and terracing are effective in preserving soil and preventing erosion.